Interferon-tau (hereinafter “IFNτ” or “interferon-τ”) was discovered originally as a pregnancy recognition hormone produced by the trophectoderm of ruminant conceptuses (Imakawa, K. et al, Nature, 330:377–379, (1987); Bazer, F. W. and Johnson, H. M., Am. J. Repro. Immunol., 26:19–22, (1991)). The distribution of the IFNτ gene is restricted to ruminants, including cattle, sheep, and goats, (Alexenko, A. P. et al., J. Interferon and Cytokine Res., 19:1335–1341, (1999)) but has been shown to have activity in cells belonging to other species including humans and mice (Pontzer, C. H. et al., Cancer Res., 51:5304–5307, (1991); Alexenko, A. P. et al., J. Interferon and Cytokine Res., 20:817–822, (2000)). For example, IFNτ has been demonstrated to possess antiviral, (Pontzer, C. H. et al., Biochem. Biophys. Res. Commun., 152:801–807, (1988)), antiproliferative, (Pontzer, C. H., et al., 1991) and immunoregulatory activities (Assal-Meliani, A., Am. J. Repro. Immunol., 33:267–275 (1995)).
While IFNτ displays many of the activities classically associated with type I IFNs, such as interferon-α and inteferon-β, considerable differences exist between IFNτ and the other type I IFNs. The most prominent difference is the role of IFNτ in pregnancy in ruminant species. The other IFNs have no similar activity in pregnancy recognition. Also different is viral induction. All type I IFNs, except IFNτ, are induced readily by virus and dsRNA (Roberts, et al., Endocrine Reviews, 13:432 (1992)). Induced IFN-α and IFN-β expression is transient, lasting approximately a few hours. In contrast, IFNτ synthesis, once induced, is maintained over a period of days (Godkin, et al., J. Reprod. Fert., 65:141 (1982)). On a per-cell basis, 300-fold more IFN-τ is produced than other type I IFNs (Cross, J. C. and Roberts, R. M., Proc. Natl. Acad. Sci. USA 88:3817–3821 (1991)).
Another difference lies in the amino acid sequences of IFN-τ and other type I interferons. The percent amino acid sequence similarity between the interferons α2b, β1, ω1, γ, and τ are summarized in the table below.
rHuIFNα2brHuIFNβ1rHuIFN1ω1rHuIFNγrOvIFNτRhuIFNα2b33.160.811.648.8RhuIFNβ133.133.112.233.8RhuIFNω160.833.110.254.9RhuIFNγ11.612.210.210.2rovIFNτ48.833.854.910.2Sequence comparison determined from the following references:Taniguchi et al., Gene, 10(1):11 (1980).Adolf et al., Biochim. Biophys. Acta, 1089(2):167 (1991).Streuli et al., Science, 209:1343 (1980).Imakawa et al., Nature, 330:377 (1987).
Recombinant ovine IFNτ (rIFNτ) is 48.8 percent homologous to IFNα2b and 33.8 percent homologous to IFNβ1. Because of this limited homology between IFNτ and IFNα and between IFNτ and IFNβ, it cannot be predicted whether or not IFNτ would behave in the same manner as IFNα or IFNβ when administered orally. IFNτ is also reported to have a low receptor binding affinity for type I receptors on human cells (Brod, S., J. Interferon and Cytokine Res., 18:841 (1999); Alexenko, A. et al., J. Interferon and Cytokine Res., 17:769 (1997)). Additionally, the fact that IFNτ is a non-endogeneous human protein generates the potential for systemic neutralizing antibody formation when IFNτ is introduced into the human body (Brod, S., J. Interferon and Cytokine Res., 18:841 (1999). These differences between IFNτ and the other interferons make it difficult to predict whether IFNτ when administered to a human will provide a therapeutic benefit. Teachings in the art relating to oral administration of IFNα, IFNβ, or any other non-tau interferon, fail to provide a basis for drawing any expectations for IFNτ.
One limiting factor in the use of IFNτ, as well as proteins and polypeptides in general, is related to biodistribution, as affected by protein interaction with plasma proteins and blood cells, when given parenterally. The oral route of administration is even more problematic due to proteolysis in the stomach, where the acidic conditions can destroy the molecule before reaching its intended target. For example, polypeptides and protein fragments, produced by action of gastric and pancreatic enzymes, are cleaved by exo- and endopeptidases in the intestinal brush border membrane to yield di- and tri-peptides. If proteolysis by pancreatic enzymes is avoided, polypeptides are subject to degradation by brush border peptidases. Polypeptides or proteins that might survive passage through the stomach are subject to metabolism in the intestinal mucosa where a penetration barrier prevents entry into cells. For this reason, much effort has been focused on delivering proteins to the oral-pharyngeal region in the form of a lozenge or solution held in the oral cavity for a period of time.